1. Field of the Invention
This invention relates to a method and apparatus for decolorizing toner images formed on a sheet from toner which can be photochemically decolorized, and also to an image forming apparatus.
2. Description of the Related Art
Recently, in view of the conservation of nature, particularly the conservation of forests and the reduction of wastes in urban areas, the reuse and regeneration of used paper have again attracted public attention. As part of such recycling, the reuse of waste copy sheets, printed matter, facsimile sheets and the like used in offices has been studied.
Since the majority of such waste paper consists of confidential documents, which are generally company secrets, however, it is very difficult to collect such waste paper outside the company to regenerate the paper. Furthermore, it is very difficult to erase recorded or printed portions of printed matter and copy sheets, and therefore printed matter and copy sheets are forced to be burned or shredded. Consequently, the general recognition is that it is substantially impossible to reuse such paper.
In view of the above, the inventors have conducted studies to find a near infrared-decolorizing pigment which absorbs near infrared rays to be decolorized, and developed a toner using such a pigment. This toner was proposed in Japanese patent application No. HEI3-277725 (1991).
When an electrostatic copy operation is conducted using that toner, images or characters formed on a sheet such as a copy sheet can be erased only by illumination with near infrared rays, and after this erasure an electrostatic copy operation or printing can be further conducted on the sheet, thereby allowing the sheet to be reused. When such used sheets are to be disposed of, recorded Images or characters can be erased only by illumination by near infrared rays. Therefore, there are many advantages, such as the sheets being collected to be reused in a company without leaking secrets to the outside.
However, the rate of decolorization when performed only by illumination with near infrared rays is low. For example, the process of decolorizing a toner image formed on the entire surface of a recording sheet of A4 size of JIS (Japanese Industrial Standard) requires several tens of seconds. Namely, this decolorizing process has a problem in that it can process only a few sheets per minute.
When an electrostatic photography copier or printer, which forms an image on a recording sheet using such a decolorizable toner, and a decolorizing means for decolorizing an image on a recording sheet to make the sheet colorless so it can be reused, are independently installed, there arises another problem in that they require a large installation space. Even if the recording has been done with using a decolorizable toner, the recording sheets cannot be reused unless the decolorizing means is available. Therefore, it is cumbersome to separately install the electrostatic photography image forming apparatus and the decolorizing means so as to be paired with each other.
A currently used electrostatic photography copier or printer and the toner therefor are constructed to function in pairs. Namely, the most suitable toner is selected for each kind of copier and printer. Therefore, there Is no toner that can be suitably and commonly used for all kinds of copiers and printers. Copiers and printers are designed and adjusted so that various toners of different characteristics achieve optimum image qualities. Even if many kinds of decolorizable toners with different characteristics become available, therefore, a decolorizable toner and electrostatic photography image forming apparatus which is designed and adjusted to be optimum for the use of that decolorizable toner must be used in pairs. Consequently, the decolorizable toner, electrostatic photography image forming apparatus and decolorizing means are realized so that their characteristics relate to each other. When electrostatic photography image forming means and decolorizing means are constructed independently of each other, it is required to separately prepare individual image forming means and decolorizing means in accordance with a decolorizable toner to be used. This involves cumbersome work. When decolorizable toner, an electrostatic photography image forming apparatus and decolorizing means are combined in an unsuitable manner, it may be impossible to form optimum images on recording sheets or to sufficiently achieve the decolorization.